<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
/*************************************/
    //const a;//报错
/*************************************/
    // const a = 30;
    // a = 40;//报错
/*************************************/
    const obj = {
        a:30,
        b:40
    }
    obj.age = 24;
    console.log(obj.age);
    obj={
        //报错
    }
</script>
</html>